1. Technical Field
The invention relates to a plain bearing element having a support layer, a preferably lead-free intermediate layer based on an aluminum alloy, and a preferably lead-free bearing metal layer based on an aluminum alloy.
2. Related Art
Such bearings are the subject of numerous documents. For example, reference is made to unexamined German applications EP 0 672 840 A2, EP 1 522 750 A1 or U.S. Pat. No. 5,470,660. The plain bearing element in the form of a bearing shell has a support shell made of steel on which a foil-like bearing metal layer or antifriction layer is applied by roll plating. Since the aluminum-based bearing metal layer that generally contains a high amount of tin cannot be plated to the steel support layer with sufficient adhesion, the bearing metal layer is initially plated with an intermediate layer by means of roll plating to form a foil laminate. Initially, an intermediate layer of pure aluminum was used that enables strong adhesion to the steel support layer. This foil laminate is then applied to the steel protective layer in several rolling steps with or without intermediate heat treatment while reducing the thickness of the layers. The finished laminate is then processed by being stamped or cut into plates and, depending on the finished product, processed into a radial bearing by bending or roll forming.
The aforementioned documents are based on the knowledge that the adhesion of the aluminum-based bearing metal layer to the steel support layer can be improved, yet the material properties of the pure aluminum intermediate layer do not ensure that the laminate has sufficient fatigue strength during operation. Consequently, EP 0 672 840 A2 proposes forming an intermediate layer based on a hardenable aluminum alloy, possibly with safety running features instead of pure aluminum foil. The hardness of the intermediate layer formed in this manner is adjusted to a value of approximately 68 HV 0.5 and is therefore higher than the hardness of the anti-friction layer that is approximately 35 to 40 HV 0.5. The hardness which decreases in the direction of the bearing metal layer or antifriction layer is intended to have a positive effect on the fatigue strength and hence on the durability and the life of the plain bearing.
U.S. Pat. No. 5,470,666 arrives at a similar result. In this case as well, the hardness increases from the plain bearing layer over the intermediate layer to the metal support layer, and the hardness of the intermediate layer is adjusted to lie between 25 HV and 60 HV. The thickness of the intermediate layer is 50 to 90% of the overall thickness of the bearing metal layer and the intermediate layer. The intermediate layer is therefore at least as thick or significantly thicker than the bearing metal layer. The intermediate layer is formed of an aluminum alloy with a total of 0.3 to 5 weight percent of alloy components selected from the group consisting of Mn, Cu, Zn, Si, Mg and Fe. The upper limit of the intermediate layer hardness of 60 HV is determined by the formability that is required to compensate for edge bearing, that is, an unavoidable misalignment between the shaft and bearing axis.